1. Field of the Invention
The present invention relates to an image display apparatus that enables a magnified view of an image formed in an original image forming unit through an optical system with convenience, and, in particular, to an image display apparatus suitable for a head-mounted display (HMD).
2. Description of the Related Art
To date, an image display apparatus is known which allows an image formed in an original image forming unit to be recognized as a magnified virtual image through an optical system, such as a lens and a concave mirror. According to a technique discussed in U.S. Pat. No. 5,982,343, part of an original image is displayed on a first display unit and the remaining part thereof is displayed on a second display unit. Then, a magnified virtual image is formed through two planar half-silvered mirrors corresponding to the respective display units and a common concave mirror. Meanwhile, U.S. Pat. No. 6,816,313 discusses a technique that enables a magnified view of an original image by illuminating pixels through a barrier element and a microlens array having lenses corresponding to respective pixels of the image in the original image forming unit. However, reduction of the optical system in size and thickness is difficult with such existing techniques, or such existing techniques provide a small viewable area, and thus a viewer is unable to view the surrounding images.
In the technique discussed in U.S. Pat. No. 5,982,343 mentioned above, the original image is divided into a plurality of pieces, and thus the effective diameters of the corresponding optical system sections are smaller compared to those in a conventional configuration. However, the image displayed on the first display unit differs at least partially from the image displayed on the second display unit, and thus a light beam from only one of the displayed images needs to reach an exit pupil position. Accordingly, the effective diameters of the optical system sections corresponding to the respective images need to be greater than a necessary exit pupil diameter D.
In the technique discussed in U.S. Pat. No. 6,816,313, since the magnified view of the image is provided by the microlens array including optical elements (i.e., microlenses) that correspond to the respective pixels of the image and apertures, the width of a light beam emitted from each microlens is small, and the viewable area is small. Thus, the viewer is unable to view the surrounding images.